首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   235325篇
  免费   2370篇
  国内免费   822篇
化学   118626篇
晶体学   4012篇
力学   10808篇
综合类   1篇
数学   25998篇
物理学   79072篇
  2020年   1845篇
  2019年   2123篇
  2018年   2757篇
  2017年   2692篇
  2016年   4029篇
  2015年   2477篇
  2014年   4071篇
  2013年   10199篇
  2012年   7739篇
  2011年   9610篇
  2010年   6820篇
  2009年   6741篇
  2008年   8885篇
  2007年   8915篇
  2006年   8442篇
  2005年   7659篇
  2004年   7029篇
  2003年   6200篇
  2002年   6138篇
  2001年   7123篇
  2000年   5393篇
  1999年   4260篇
  1998年   3577篇
  1997年   3493篇
  1996年   3321篇
  1995年   3026篇
  1994年   2966篇
  1993年   3056篇
  1992年   3159篇
  1991年   3347篇
  1990年   3097篇
  1989年   3032篇
  1988年   3074篇
  1987年   2960篇
  1986年   2803篇
  1985年   3819篇
  1984年   4014篇
  1983年   3203篇
  1982年   3415篇
  1981年   3339篇
  1980年   3233篇
  1979年   3335篇
  1978年   3424篇
  1977年   3354篇
  1976年   3448篇
  1975年   3142篇
  1974年   3152篇
  1973年   3194篇
  1972年   2235篇
  1971年   1849篇
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
61.
Exosomes are nanovesicles secreted by most cellular types that carry important biochemical compounds throughout the body with different purposes, playing a preponderant role in cellular communication. Because of their structure, physicochemical properties and stability, recent studies are focusing in their use as nanocarriers for different therapeutic compounds for the treatment of different diseases ranging from cancer to Parkinson's disease. However, current bioseparation protocols and methodologies are selected based on the final exosome application or intended use and present both advantages and disadvantages when compared among them. In this context, this review aims to present the most important technologies available for exosome isolation while discussing their advantages and disadvantages and the possibilities of being combined with other strategies. This is critical since the development of novel exosome‐based therapeutic strategies will be constrained to the effectiveness and yield of the selected downstream purification methodologies for which a thorough understanding of the available technological resources is needed.  相似文献   
62.
Physics of Atomic Nuclei - The paper presents a comparison of three neutrons identifying methods in scintillators based on ZnS with 6Li and 10B: charge integration method, pulse gradient analysis,...  相似文献   
63.
64.
Journal of Applied Spectroscopy - Aqueous solutions of human hemoglobin have been studied by the multi-angle static light scattering method. The tendency of sickle-shaped erythrocytes to aggregate...  相似文献   
65.
Crystallography Reports - Nd1 – yEuyF3 – y crystals (y is the molar fraction of EuF2; 0 ≤ y ≤ 0.15) with a tysonite (LaF3) structure have...  相似文献   
66.
Optics and Spectroscopy - The optical absorption spectra of zinc oxide (ZnO) thin films formed by reactive cathode sputtering are studied. The observed absorption of light in the region of photon...  相似文献   
67.
The biomimetic sol—gel synthesis of silicon—chitosan-containing glycerohydrogels was carried out using silicon tetraglycerolate as a precursor. It was found that chitosan accelerates gel formation in weakly acidic media. In more acidic media, the kinetics of the process changes according to the curve with a maximum, which can be attributed to different mechanisms of silanol condensation before and after the isoelectric point. The investigated silicon—chitosan-containing glycerohydrogels exhibit antibacterial, anti-inflammatory, and wound healing activity. The synthesized hybrid glycerohydrogels are promising materials for biomedical applications.  相似文献   
68.
Russian Journal of General Chemistry - Thermogravimetry, differential scanning calorimetry, and flow methods were used to investigate thermal properties of a series of cobalt(II)...  相似文献   
69.
Russian Journal of General Chemistry - The technical legal acts that regulate the quality and safety parameters of mineral waters out were analyzed. Seven samples of mineral waters produced in...  相似文献   
70.
In this review, methods to obtain the orientational order of topologically variant molecular mesogens using by one- and two-dimensional (2D) solid-state 13C nuclear magnetic resonance (NMR) spectroscopy are described. Besides 13C chemical shifts, the 13C─1H dipolar couplings measured from 2D-separated local field (SLF) technique are used for computing the order parameters of a variety of mesogens. The investigated molecules are composed of a variable number of rings in the core, that is, core ranging from simply one ring to five rings. Among the mesogens investigated, a special focus has been placed on mesogens with thiophene rings, which are gaining popularity as liquid crystalline organic semiconductors. The replacement of a phenyl ring by thiophene in the core has a dramatic influence on molecular topology, as observed from the measured order parameters. The review highlights the advantages of the 2D SLF method for understanding the local dynamics and for mapping the topology of mesogens through the measured order parameters. SLF NMR studies of as many as 24 molecular mesogens that vary in terms of the molecular structure as well as topology are covered in the review. Order parameters of the rings have been estimated from the 13C─1H dipolar couplings in the nematic, smectic A, smectic C, and tilted hexatic phases as well as in B1 and B2 mesophases of various mesogens. It is anticipated that, in the years to come, the 2D SLF method would provide advanced molecular information on structurally complex mesogens that are emerging in liquid crystal science through the incessant efforts of synthetic chemists. The mini review covers the orientational order of topologically variant molecular mesogens determined by 1D and 2D solid-state 13C NMR spectroscopy. Accordingly, rod-like, bent-core, and thiophene mesogens were subjected to 2D SLF measurements to get the order parameters from which the topology was established. The replacement of phenyl ring by thiophene and its influence on order parameters as well as on molecular topology is also discussed.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号